The invention relates to a humidifier for producing humidified air, and particularly, although not exclusively, to a humidifier for use with a Continuous Positive Airway Pressure (CPAP) device.
A CPAP device is used in the treatment of obstructive sleep apnea syndrome, which is a disorder characterised by cycles of snoring, obstruction of the upper airway, and partial awakening during the night. In order to treat obstructive sleep apnea, a CPAP device can be used to deliver air under continuous positive pressure to the nasal passages of the patient during sleep. The positive air pressure prevents obstruction of the upper airway so that the patient is not troubled by frequent awakenings during sleep.
In order to prevent drying of the patient""s airway during use of a CPAP device, it is known to pass the air through a humidifier before supplying the air to the patient. Humidification can be achieved by simply passing the air over an area of water within a humidifier so that the air absorbs moisture from the water before being delivered to the patient.
When a humidifier is used with a CPAP device, it is convenient to be able to place the CPAP device on top of the humidifier. In this case, it is desirable that the humidifier is designed so as to form a low, generally flat base for supporting the CPAP device. Such a humidifier is known as a low-profile humidifier. Because a low-profile humidifier is of low height, it is more likely to suffer from the problem of entrainment of water droplets in the output air flow to the patient. This problem arises because as the air passes through the humidifier it induces waves on the surface of the water, and water droplets are stripped from the waves by the air flow, and carried by the air flow to the outlet of the humidifier. It is also important when designing a low-profile humidifier to ensure that maximum use is made of the available water surface area. For example, there is no point in providing a large surface area of water within the humidifier if the air flow passes over only a small portion of this area.
The present invention has arisen from attempts to overcome the above difficulties, but is not limited to low-profile humidifiers, or to humidifiers for use with CPAP devices.
According to the invention there is provided a humidifier for producing humidified air, comprising an air inlet for receiving air to be humidified, an air outlet for discharging humidified air, and an elongate passageway, extending between the air inlet and air outlet, for directing air from the air inlet to the air outlet, the passageway being adapted to be partially filled with water so that air passing along the passageway becomes humidified as it passes over the water from the air inlet to the air outlet.
The use of an elongate passageway between the air inlet and outlet ensures that the airflow passes over substantially the whole of the surface area of the water, so that the whole of the surface area of the water contributes towards humidifying the air flow.
Preferably, the passageway is arranged so as to direct the air from the air inlet to the air outlet along a single path.
This feature ensures that each portion of the surface area of the water contributes equally to the humidifying of the air flow. In an arrangement where the air flow can take a number of different paths between the air inlet and the air outlet, there is a danger that certain paths will contribute more greatly to the humidifying process than others, for example because the air is flowing at different speeds along different paths. Such an arrangement does not make maximum use of the available water surface area.
In a preferred embodiment of the invention, the passageway is divided into a plurality of elongate subpassageways and corner portions, each subpassageway being substantially straight, and the subpassageways being connected end to end along the length of the passageway by the corner portions.
The subpassageways can be integrally formed with the corner portions, so that the passageway as a whole is integrally formed.
This feature avoids the possibility of leaks which might otherwise occur at the connections between the subpassageways and corner portions.
One or more of the corner portions can be generally U-shaped, so that the two subpassageways adjacent the or each generally U-shaped corner portion lie side by side, and substantially parallel with each other.
For example, if the passageway is divided into two, three or four subpassageways, the subpassageways can be arranged to form U-, S- or W-shaped serpentine passageways respectively.
It will be appreciated that the use of generally U-shaped corner portions enables the humidifier to be of compact construction, since the subpassageways lie side by side. This allows a greater number of subpassageways to be accommodated within a humidifier of a given size.
Preferably, the passageway is provided with at least one generally U-shaped corner portion which bulges outwardly at the inside side of the corner defined by the corner portion so as to force air passing through the corner portion outwardly towards the outside side of the corner defined by the corner portion.
This feature ensures that substantially the whole of the surface area of the water in the corner portion is used for humidifying the air flow.
The last corner portion through which air passes before reaching the air outlet will be referred to below simply as xe2x80x9cthe last corner portionxe2x80x9d.
Desirably, the last corner portion, whether or not generally U-shaped, increases in width as it passes from the penultimate subpassageway to the last passageway.
It should be understood that the word xe2x80x9cwidthxe2x80x9d used above is intended to refer to the dimension of the passageway which lies generally in the plane defined by the surface of the water, and perpendicular to the direction of the air flow along the passageway. Furthermore, the xe2x80x9clastxe2x80x9d subpassageway is the last passageway through which air in the humidifier passes before reaching the air outlet. The advantage of increasing the width of the passageway at the last corner portion is that it reduces the amount of turbulence in the air flow at the corner portion. It should be noted that most of the air turbulence within the passageway is created at the corner portions, and this turbulence is particularly acute in the case of U-shaped corner portions. The air turbulence creates waves on the water surface which can result in entrainment of water droplets in the air flow at the air outlet, or, if the waves are large enough, indirect spillage of water into the air outlet. By reducing the air turbulence at the last corner portion, the chances of water spillage, or entrainment of water droplets, at the air outlet are greatly reduced.
Preferably, the width of the last corner portion increases gradually as the last corner portion passes from the penultimate subpassageway to the last subpassageway.
Such a gradual increase causes a greater reduction in air turbulence at the corner portion.
In one embodiment of the invention, the ratio of the width of the last corner portion at its inlet side to its width at its outlet side is 9:10.
Preferably, the upper wall, or roof, of the last subpassageway rises gradually along the length of the last subpassageway, towards the air outlet, so as to allow the air outlet to be positioned at a greater height above the water within the last subpassageway.
The gradual increase in height of the roof of the last subpassageway results in a smooth air flow and less air turbulence.
Ideally, the roof of the last subpassageway rises gradually along substantially the whole length of the last subpassageway,.
Similarly, the roof of the first subpassageway may rise gradually along the length of the first subpassageway, towards the air inlet, in the same manner as the roof of the last subpassageway.
In a preferred embodiment of the invention, the passageway terminates at an end wall adjacent the air outlet, and the air outlet is arranged so that it communicates with the interior of the passageway at a location which is spaced away from said end wall.
When the air flow within the passageway creates waves on the surface of the water, it has been found that the water has a tendency to splash against the end wall of the passageway, resulting in a danger of water spilling into the air outlet. It has been found that by spacing the air outlet aperture away from the end wall, the danger of water spilling into the air outlet is greatly reduced.
In a second aspect of the invention there is provided a humidifier for producing humidified air, comprising a chamber adapted to be partially filled with water, the chamber being provided with an air inlet for receiving air to be humidified, and an air outlet for discharging humidified air from the chamber after the air has passed over said water, wherein the air outlet is arranged so that it communicates with the interior of the chamber at a location which is spaced away from all of the chamber walls.